I use paper towel for my leopard geckos. Its not because of impaction reasons, its mainly because it is EXTREMELY easy to clean, keep clean, and keep tabs on feeders ect. I dont condone using particle substrates for Leopard Geckos, but using a particle substrate while practicing proper supplementation and husbandry will generally not lead to impaction. I would never house a baby or a juvenile Leo on a particle substrate, period.
For the bearded dragon, I am keeping it on paper towels right now, but i will probably move to slate when i move it into the 75 gallon enclosure.